Linear protection switching is known which couples a node apparatus and a remote node apparatus at the other end of the connection via redundant paths which include a working path and a protection path. In one method of linear protection switching, control information for controlling the protection switching is stored in a data frame of a prescribed format which is transferred over a working path or a protection path between node apparatuses. A data frame carrying such protection switching control information will hereinafter be described as the “control frame.” An APS (Automatic Protection Switching) frame is an example of the control frame.
One implementation of such linear protection switching employs a method that prescribes that the control frame be transmitted over a fixed protection path predetermined in the initial setup and if the control frame is received via a working path, it is determined that an erroneous path setting is detected. The expression “erroneous path setting” here means that there is a discrepancy in the working/protection path setting between the node apparatuses at both ends coupled via the redundant paths.
Some linear protection switching methods support a non-revertive mode. In the non-revertive mode, once working traffic is switched to the protection path due to a failure of the working path, the traffic continues to transfer over the protection path, even if the working path is thereafter restored from the failure.
One example of the linear protection switching that employs the erroneous path setting detection method and that supports the non-revertive mode is Ethernet (registered trademark) Linear Protection Switching defined in ITU-T Recommendation G.8031. In Ethernet (registered trademark) Linear Protection Switching, control information for controlling the protection switching is transferred by storing it in an Ethernet (registered trademark) OAM (Operations, Administration, and Maintenance) frame called the APS frame.
In the prior art, a line identifying method for identifying each line in a system provided with a plurality of working lines and at least one protection line for transferring frames, each having a layer-structured header, between a terminal station and a relay station or between relay stations, wherein line switching is performed using a linear APS mechanism has been proposed. This method includes: an assigning step for assigning a code indicating an APS mode to each of the working and protection lines; a first creating step for creating a request frame for evaluating the condition of each line; a first transmitting step for transmitting the request frame via each line to a station at the other end of the line; a second creating step for creating a response frame based on the assigned code when responding to the request; a second transmitting step for transmitting the response frame via each line; a determining means that determines that a failure has occurred when the code contained in the received response frame does not match the assigned code.
Alternatively, the above method includes: an assigning step for assigning a trace byte to each of the working and protection lines; a creating step for creating a frame containing the assigned trace byte; a transmitting step for transmitting the frame via each line to a station at the other end of the line; and a determining step for comparing the frame byte contained in the received frame with the trace byte assigned to the corresponding line and for determining that a failure has occurred when the frame bytes do not match each other.
A method of packet communication between nodes in a network has also been proposed. In this method, a working communication path or a protection communication path that pass through two switching nodes is selected, and while transferring first traffic between the two switching nodes by using the selected communication path, the two switching nodes transfer via the protection communication path a switching control packet, containing working path identification information, that indicates whether or not the first traffic is flowing on the working communication path. If the working communication path is operating normally, the switching nodes select the working communication path as the communication path for the first traffic, but if the working communication path is faulty, the protection communication path is selected. A protection node located along the protection communication path, i.e., a node other than the switching nodes, checks the working path identification information contained in the switching control packet and determines whether or not the first traffic is flowing on the working communication path, and if the first traffic is flowing on the working communication path, second traffic, which is different from the first traffic, is deposited into the protection node which then transfers the second traffic to another protection node.
ITU-T Recommendation G.8031 defines the signaling of a control signal for performing automatic protection switching (APS) in the Ethernet (registered trademark) Linear Protection Switching.
Related art is disclosed in Japanese Unexamined Patent Publication No. 2003-298474, Japanese Unexamined Patent Publication No. 2008-104144, ITU-T Recommendation G.8031/Y. 1342 and ITU-T Recommendation G.8031/Y. 1342 Amendment 1.